It has become very common to download contents from a network for use in a mobile device such as a cellular phone or personal digital assistant (PDA). Various types of contents, including game applications, moving pictures and/or video images, wallpapers, and ringing melodies, can be downloaded. In addition, private data such as schedules or telephone directories can be created in mobile devices.
Downloaded contents and/or created data (collectively referred to simply as “data” or “user data”) are stored in the memory of an individual mobile device. If the mobile device is lost or broken, such contents and/or data stored in the mobile device cannot be used in a new mobile device. If the user wants to continuously use content having been downloaded in the lost or broken mobile device, the same content has to be acquired again. In many cases, an extra fee is required to re-download the same content, and such inconvenience impairs user-friendliness. A more serious problem is that the data created in a mobile device cannot be completely re-created.
To deal with these problems, a data management service system for cellular phones is proposed (see, for example, Patent Document 1 listed below). In the data management service system, the data used in a mobile device are backed up in the system to solve the inconvenient problem that the data having been used in the mobile device cannot be continuously used in a new device upon replacement of the mobile device. The user data for use in the mobile device are uploaded in a data management server on the network, and desired data are downloaded in the mobile device from the server as necessary. Accordingly, the contents or private data can be continuously used even if the mobile device is replaced with a new one.
With this data management service system, not only the data freely used in the mobile device, but also copyright-protected data can be backed up in the system. Data items furnished with creators' (or copyright owners') ID information are stored in a copyright-protected area in the server, and restricted to be moved to other memory areas. Downloading of each of the data items in the copyright-protected area is permitted only for authorized mobile device(s) that are managed in association with that data item.
Another known technique is a contents backup method (see, for example, Patent Document 2 listed below). When copyright-protected content is delivered, a backup server is designated, which server is authorized in advance as a content backup site. The delivered content is authorized to be backed up only in the designated backup server.    [Patent Document 1] JP (Kokai) 2004-200845 A    [Patent Document 2] JP (Kokai) 2004-48180 A